Carter returns from Africa, going straight to Abby's bedside. Her response to seeing him is to ask for her key back. She is very chilly towards him all day until new med student Neela Rasgotra answers a phone call for Carter. The message: Luka is dead. Carter decides to go back to the Congo to bring the body back. Neela has a tough first day in the ER, earning Chen's ire after Pratt flirts with her. Gallant, now a full-fledged doctor, helps to show her the ropes.

Luka Kovac arrives safely at County General and is hospitalized for treatment. His friend Gillian delivers John Carter's letter to Abby.

Confident second-year resident Pratt wants to prove his abilities when he works the graveyard shift (11 p.m. to 7 a.m.), but his heroics sometimes backfire. Pratt shows contempt for a man, Ed Gamble, who presents no symptoms of disease but temporarily loses his speech.

Ben Hollander is a distraught architect whose degenerating eyesight causes him despondent while a spirited new nurse, Samantha Taggart joins the staff. Elsewhere, disaster strikes when the doctors suspect a mother is abusing her child while Dr. Corday learns something shocking about the charismatic Dr. Dorset, and Dr. Archie Morris is overwhelmed by the chaos and grisly conditions of life in the E.R.

Pratt and Kovac clash over a miscarriage-prone young woman, Denny, who arrives to deliver a premature baby. Pratt wants to make heroic efforts to save the unborn child, while Kovac is adamantly against spending vast amounts of money to keep the forever sickly baby alive.

To everyone's amazement, Lewis makes a date to share a home-cooked dinner with the elderly Ben Hollander, her depressed patient who is going blind.

On Thanksgiving Day, a helicopter crash outside the ER leaves several injured, and kills Dr. Romano. Alex tries to bring Sam and Luka together.

Neela helps treat two Amish teens who were in a car crash. Sam argues with Dr. Kovac when he pays too much attention to her son.

Dr. Carter celebrates Christmas at a clinic in the Congo dealing with low supplies and anti-Americanism, but in the meantime, falling for an AIDS worker named Makemba.

Carter returns to County General to hearty welcomes. Although Abby is shocked to learn that Carter's beautiful African girlfriend, Kem, is already pregnant with Carter's child, Abby has moved on with her life as well, going back to medical school.

Abby and Neela are assigned to a month-long rotation in the neonatal intensive care unit where they experience emotional roller coasters while caring for the sick infants.

Dr. Carter's girlfriend makes an impression as she observes ER operations. Dr. Gallant is almost shot during a domestic incident. Dr. Weaver dedicates a center to the memory of Dr. Romano.

Sam treats an abused, pregnant teen. Dr. Carter introduces African girlfriend Makemba to wintertime. ER chaos shocks a risk-assessment expert. Dr. Pratt and Abby restrain a man who has tuberculosis.

Carter misses his pregnant girlfriend who has returned to Africa. A family of four is rushed to the emergency room after suffering carbon monoxide poisoning from their faulty furnace--forcing the claustrophobic Neela to accompany a newborn baby into an extremely uncomfortable hyperbaric chamber.

Morris streets a patient without getting a psych consult, and the guy steals a tank and heads for County. Gillian is visiting Luka, and Sam's not happy about it. Luka and Sam make up by the end of the day though. A 13-year-old boy has chlamydia. Frank has a heart attack. Corday plays the dating game, going out with two men.

Carter sticks up for Neela when the other attendings doubt her future in the ER. Neela caves to the pressure and accidentally gives a patient the wrong medication. Gallant takes the blame for her though. Sam and Luka try to plan Alex's birthday party. Frank visits on his way to therapy. Chen's home nurse quits after her dad behaves poorly.

Weaver rushes to the aid of her female life partner, Sandy Lopez, when the firefighter is severely injured while working and must now battle for her life. Frightened Weaver whispers hope to Sandy by reminding the victim of their newborn child.

Pratt struggles to diagnose a woman who suffers mysterious chronic seizures. An attractive woman, Campbell, informally accuses flirtatious Pratt of sexual harassment. Abby ponders how to get her contentious patients' attention during her psychiatric department rotation.

A panic-stricken Weaver is ordered to give her son to the Lopez family. Carter greets the returning Kem, but their meeting with his father, Jack, gets tense after Carter announces plans for his grandmother's estate.

Carter takes Kem to the hospital to check on their baby since it's not kicking anymore.

Kovacs stops to help a woman and her son whose car broke down. Steve is getting close to Alex, and Sam panics. Abby is looking for her letter whether to see she passed her boards. Pratt shows off his new Chrysler. Elgin tries to build a connection between him and Pratt. Jing-Mei might be battered by her senile father.